A boiling water reactor (BWR) which is used at a nuclear power plant is known to a person with knowledge within the field. In a BWR the core consists of a large number of fuel assemblies. Each fuel assembly contains, inter alia, a bundle of fuel rods, which contain the fissile nuclear fuel material. The bundle is surrounded by a fuel channel. When such a fuel assembly is used in a BWR, water flows through the fuel channel. The water is brought to boiling by the heat which is generated through the nuclear reaction. Through this process a relatively high pressure is formed in the fuel channel. The walls of the fuel channel may therefore tend to bulge outwards. This can have negative consequences. Between several fuel assemblies, control rod blades are inserted in order to control the nuclear reaction. If the walls of the fuel channel bulge outwards, the walls may press against such an inserted control rod blade. It may therefore become difficult to pull out the control rod blade when desired.
A further problem which can be mentioned is that which is called shadow corrosion. Shadow corrosion is a phenomenon within this technical field. Shadow corrosion may occur in a nuclear reactor. In particular, shadow corrosion may occur on components of Zr or Zr-based alloys when such components come into contact with (or are positioned at a very short distance from) components of other materials, such as of stainless steel. The fuel channel is normally made of a Zr-based alloy, while the control rod blades often are made of stainless steel. If the fuel channel bulges outwards, a larger area of the walls of the fuel channel may thus come into contact with (or be positioned very close to) the control rod blades, which can cause shadow corrosion to potentially occur on the fuel channel.
U.S. Pat. No. 5,253,278 describes a fuel assembly which comprises a fuel channel which surrounds a bundle of fuel rods. The fuel channel is provided with a number of “reinforcing tabs”.
U.S. Pat. No. 4,749,543 describes a fuel assembly with a fuel channel which may be provided with longitudinal or transversal grooves. The fuel channel can also have particularly thick corner sections.
Japanese Patent Document No. JP 9-145 874 shows fuel assemblies with a fuel channel which may have an L-shaped piece which is attached by welding in a corner.
International Patent Publication No. WO 2010/110721 A1 describes a fuel assembly with a fuel channel which is provided with a number of protrusions on the side. The document also describes the problem with shadow corrosion.